The present invention relates to a control system for a combinatorial weighing or counting apparatus.
There have been used combinatorial weighing apparatus which operate by supplying articles to be weighed to weighing hoppers associated respectively with weighing machines, effecting a combinatorial operation on weights from the weighing machines with an arithmetic control unit, and opening the weighing hoppers of those weighing machines which give an optimum combination of added weights closest to a target weight as a result of the combinatorial operation, thus discharging the articles representing the optimum combination of added weights.
In the combinatorial weighing apparatus, the weighing hoppers which have discharged the articles, are immediately supplied with articles for a next weighing cycle from pool hoppers disposed above the weighing hoppers. The pool hoppers are supplied with distributed articles from a storage unit by means of an electromagnetic feeder. FIG. 1 of the accompanying drawings shows in block form such combinatorial weighing apparatus. Designated at 1 are a plurality of weighing machines W1 through Wn which issue weight values X1 through Xn (analog signals) to a multiplexer 2. When an arithmetic control unit 4 comprising a computer applies a signal S to the multiplexer 2 in response to a timing signal T from a packaging machine 5, the weight signals applied to the multiplexer 2 are successively fed to an A/D converter 3. The weight signals are converted by the A/D converter 3 into digital signals which are applied to the arithmetic control unit 4. The arithmetic control unit 4 stores the digital signals in a memory 6, reads a necessary command from the memory 6, effects combinatorial additions to find combinations of total weight values, compares the weight combinations with a target weight value Xs, and determines a combination of total weights which is closest to the target weight value Xs. If the combination of total weights does not exceed an upper weight limit setting Xu, then this combination of total weights is used as an optimum combination. With the optimum combination produced, the arithmetic control unit 4 applies a control signal C to a weighing machine driver 7 such as for the weighing hoppers or a discharge device, and then applies control signals to the electromagnetic feeder, the pool hoppers, and the weight hoppers.
Where the control system is composed of a central processing unit (CPU), and when the CPU runs out of control due to a noise signal, for example, the CPU is required to be reset by itself. However, no effective means has heretofore been available for resetting the CPU by itself. More specifically, a microcomputer generally starts its operation by reading a command from a ROM (read-only memory) into a CPU, as illustrated in FIG. 2 of the accompanying drawings.
When the CPU issues address signals to an address bus in the order to be executed, the ROM automatically delivers an instruction word to a data bus. Since the combinatorial weighing apparatus has an electromagnetic feeder actuated by SCRs (thyristors) which are phase-controlled, an electric noise signal tends to be applied to the CPU, so that a wrong instruction word is read. For example, where there are instruction words 1 through 4 composed by 3 bytes, 2 bytes, 2 bytes, and 3 bytes, respectively, as shown in FIG. 3(a), the instruction word 2 may be read as a 3-byte instruction word, as shown in FIG. 3(b), or an addressing command such as a CALL command or a JUMP command may be read in error, whereupon the microcomputer system will not operate properly.
In such a combinatorial weighing apparatus, a single computer controls the amount of articles to be supplied to the weighing machines from feeders, opening and closing of hoppers such as pool hoppers and weighing hoppers, zero point and span adjustments, and sampling of weighed values of articles in the weighing machines, and executes a combinatorial arithmetic operation. For this reason, when a new operating function is added to the computer, the function is processed only sequentially by the computer with a reduction in an entire processing capability of the computer. As a result, the combinatorial weighing apparatus does not have flexibility for alterations in design and specification, and the manufacturing cost thereof is expensive.